Behavior Of Colloidal Suspensions Research Articles

Aggregation and gelation in a tunable aqueous colloid–polymer bridging system

We report a colloid-polymer model system with tunable bridging interactions for microscopic studies of structure and dynamics using confocal imaging. The interactions between trifluoroethyl methacrylate-co-tert-butyl methacrylate copolymer particles and poly(acrylic acid) (PAA) polymers were controllable via polymer concentration and pH. The strength of adsorption of PAA on the particles, driven by pH-dependent interactions with polymer brush stabilizers on the particle surfaces, was tuned via solution pH. Particle-polymer suspensions formulated at low pH, where polymers strongly adsorbed to the particles, contained clusters or weak gels at particle volume fractions of ϕ = 0.15 and ϕ = 0.40. At high pH, where the PAA only weakly adsorbed to the particle surface, particles largely remained dispersed, and the suspensions behaved as a dense fluid. The ability to visualize the suspension structure is likely to provide insight into the role of polymer-driven bridging interactions in the behavior of colloidal suspensions.

Steady azimuthal flow field induced by a rotating sphere near a rigid disk or inside a gap between two coaxially positioned rigid disks

Geometric confinements play an important role in many physical and biological processes and significantly affect the rheology and behavior of colloidal suspensions at low Reynolds numbers. On the basis of the linear Stokes equations, we investigate theoretically and computationally the viscous azimuthal flow induced by the slow rotation of a small spherical particle located in the vicinity of a rigid no-slip disk or inside a gap between two coaxially positioned rigid no-slip disks of the same radius. We formulate the solution of the hydrodynamic problem as a mixed-boundary-value problem in the whole fluid domain, which we subsequently transform into a system of dual integral equations. Near a stationary disk, we show that the resulting integral equation can be reduced into an elementary Abel integral equation that admits a unique analytical solution. Between two coaxially positioned stationary disks, we demonstrate that the flow problem can be transformed into a system of two Fredholm integral equations of the first kind. The latter are solved by means of numerical approaches. Using our solution, we further investigate the effect of the disks on the slow rotational motion of a colloidal particle and provide expressions of the hydrodynamic mobility as a function of the system geometry. We compare our results with corresponding finite-element simulations and observe very good agreement.

High optical nonlinearity of nematic liquid crystal doped with graphen oxide

Colloidal suspensions of nematic liquid crystal (NLC) doped with graphene oxide (GO) were prepared and their third-order nonlinear optical (NLO) response χ(3), nonlinear refractive index (NLR), and nonlinear absorption coefficient (NLA) were investigated using Z-scan technique employing He: Ne laser at 632.8nm. GO doped system exhibits a significantly different nonlinear optical response compared to pure NLC and the highest nonlinearity was observed at the system including 0.75% GO.The results of GO doped NLC show that the external field changes the NL parameter are dependent upon the electrical field direction since it affects the director axis, n→, compared to their initial orientation. The external field is applied perpendicular to the cell surface. The χ(3) change value was measured as the applied electrical filed varies. The mentioned studies were carried out without and under the electric field effect using different AC voltages. The value of NLO, NLA and χ(3) in present of electric field were more significant compare without of electric field. Additionally, the optical limiting (OL) behavior of colloidal suspensions was investigated. The obtained results provide new useful information about the NLO properties of NLC's nanocomposite in particular to design optical limiting devices and also other photonic applications.

Control of Rheology and Sedimentation Behavior of Colloidal Suspensions

To establish the preparation method of colloidal suspensions with low viscosity and long term stability against sedimentation, the effects of polymer and surfactant are examined for silica suspensions. The suspensions are flocculated by bridging mechanism, in which one polymer chain is simultaneously adsorbed onto two particles. Since the adsorption affinity of polymer for the silica surfaces is governed by a balance between polymer and surfactant concentrations, two bridging conformations, that is, the reversible bridging and irreversible bridging are induced. In suspensions flocculated by reversible bridging, the interparticle bonds are constantly forming, breaking, and re-forming in a quiescent state and the suspensions behaves as fluids even at very low shear rates. The sedimentation stability is evaluated through the time dependence of intensities of backscattering lights from the suspensions. The fluctuation of backscattering intensity is detected for suspensions flocculated by reversible bridging. The local motion and rearrangement of particles may be possible in the sediment. The reversible bridging is very attractive as a new technique of controlling the viscosity and sedimentation stability of flocculated suspensions.

New Developments in Colloid Science

AbstractThis introductory article reviews the topics covered in this issue of MRS Bulletin on New Developments in Colloid Science. Colloidal particles have a long history of importance in a broad range of applications in technology and materials processing. They can be made from many different materials and suspended in a wide variety of solvents. The rheological properties of colloidal suspensions have traditionally been of primary concern in their technological applications, and our understanding of these properties continues to evolve. However, new uses of colloidal particles are also emerging. Because they can be produced to a precise size, colloidal particles are now also being used in novel ways as building blocks for engineering completely new materials, including high-precision filters, controlled-porosity substrates, and photonic devices. In addition, new methods are evolving to alter the shape of the particles and create controlled structures with nonspherical particles. New experimental techniques are allowing improved measurement and increased understanding of the structure, properties, and behavior of colloidal suspensions. Significant progress continues to be made, and the potential uses of colloidal particles continue to grow. This issue presents a snapshot summary of recent developments in this field.

Stability and ocular tolerance of cyclophosphamide-loaded nanospheres

The physical and chemical stabilities of several formulations of cyclophosphamide-loaded polybutylcyanoacrylate (PBCA) nanospheres developed for an ophthalmic application as an immunosuppressive agent were studied over 6 months of storage at 4, 25 and 40°C in different experimental conditions. The physical stability of nanospheres was followed by the study of morphological (visual appearance) and morphometrical properties (mean particle size and polydispersity). The pH and tonicity of the suspensions and the association efficiency of the drug to polymeric system were also analysed to evaluate their chemical stability. The behaviour of colloidal suspensions with storage conditions was also followed by differential scanning calorimetry. The degradation of PBCA was affected by temperature and pH. The average particle size of all nanospheres remained practically unchanged throughout the study, with the polydispersity index being less than 0.1, corresponding to a monodisperse system. At 40°C, a loss of 25.9% of the initial association efficiency, especially in non-buffered pH 7.2 medium, was observed. The type of polymer degradation (surface erosion) was also determined by photon correlation spectroscopy. The results obtained from in vivo study of ocular tolerance indicate a good ocular tolerance for drug loaded to nanospheres.

Numerical and approximate studies on the theoretical dielectric relaxation of colloidal suspensions in the time domain

In this work we show numerical calculations on the dielectric behavior of colloidal suspensions in the time domain. The theory elaborated by DeLacey and White ((1981) J Chem Soc Faraday Trans 2 77:2007–2039) for dilute suspensions in the frequency domain, will be the basis for the present study. The different contributions, and their relative importance, to the transient current density generated in the suspensions after the application of a step electric field, are calculated from the dielectric response function associated to the DeLacey and White's model. In particular, we analyze the conduction and absorption current densities in the transient states upon changing the concentration of the supporting electrolyte in the suspension. With the aim of characterizing the response of the suspension for short times, an approximation to the distribution function of relaxation times that best fits the dielectric model, is calculated. Finally, an exhaustive analysis of the behavior of the dielectric response function is carried out, together with a comparison with other models in the time domain.

Buckling of a Confined Colloidal Crystal

AbstractThe behavior of colloidal suspensions confined between two plates narrowly spaced is examined. When plate separations are small, only one layer of particles can be confined; however, as plate separation is increased, multiple layers will eventually form. These layers can exist in a variety of structures depending on the energetics of packing. We examine the unstable modes which form as a single layer buckles on its way to forming two layers. Three ordered states are found; which one is selected depends on the form of the interparticle and wall potentials.

Suspensions and Sediments. Part I. Particle-Particle Interactions in Dilute Solid-Liquid Suspensions

Abstract This article gives a general review of sedimentation behavior relating to dilute suspensions of solids in liquids. There is a strong assumption that partial-fluid association is the factor responsible for variations of sedimentation behavior from one suspension system to another. Studies are therefore cited to acquire an understanding of the hydrodynamic interactions between the solids and liquids within suspensions. Behavior of colloidal suspensions is also included, and the effects of such factors as liquid dielectric constant, charge density, and electrical potential on the interaction of particles are discussed.

The Behavior of Colloidal Suspensions with Immiscible Solvents

The Behavior of Colloidal Suspensions with Immiscible Solvents